This invention relates to a sintered glass-powder product obtained by sintering a molded member of crushed glass powder.
The sintered glass-powder product is effectively utilized in fabricating such insulating materials as multilayer wiring substrates on which many highly integrated LSI's are mounted, because the product can be prepared and sintered together with low-resistance alloys or metals such as silver, silver-palladium, gold or the like.
Because of an increasing demand for miniaturization and the higher reliability of multilayer wiring substrates on which many elements including highly integrated LSI's are mounted, multilayer wiring substrates made of ceramic material have been increasingly utilized. In fabricating such a multilayer wiring substrate, a conductor wiring pattern of Mo, W, or a similar metal having a high melting point is initially print-molded by means of a known thick-film technique into the shape of a green sheet with alumina as a main component. A plurality of such green sheets are then stacked and joined into a multilayer green sheet assembly, and the assembly is sintered within a non-oxidizing atmosphere at a high temperature of about 1,500.degree. to 1,600.degree. C.
The foregoing multilayer wiring substrate having alumina as its main component has been unsuitable for high speed signal processing because of the relatively high dielectric constant of alumina and because the very thin wiring pattern of a metal high in resistance and melting point make the transmission time of signals propagating through the wiring pattern of the substrate too long. It may be possible for the metal high in resistance and melting point to be replaced by a lower resistance metal or alloy such as Au, Ag, Ag-Pd, Cu or the like in forming the wiring pattern. Since the low resistance metal material generally has a melting point of about 1,000.degree. C. or less, which is much lower than the sintering temperature of alumina, there arises the problem that the wiring pattern cannot follow any shrink of the green sheet during the sintering of the sheet so as to result in an open-circuiting of the conductor wiring.
In using the low resistance metal material for high speed signal processing, on the other hand, there has been suggested a multilayer wiring substrate of a sintered glass-powder product (glass ceramic product) for eliminating the foregoing problem, as disclosed in, for example, U.S. Pat. No. 4,301,324 to Ananda H. Kumar et al. and U.S. Pat. No. 4,413,061, a division of the former. There, a raw material containing 48 to 55 wt % of SiO.sub.2, 18 to 25 wt % of Al.sub.2 O.sub.3, 18 to 25 wt % of MgO, a small amount of nucleant selected from a group consisting of ZnO, P.sub.2 O.sub.5, TiO.sub.2, SnO.sub.2 and ZrO.sub.2, and less than 4 Wt % of B.sub.2 O.sub.3 are sintered at a temperature of 925.degree. to 1,050.degree. C. so that microcrystalline networks of alpha-cordierite are generated with the residual glass containing microcrystalline clinoenstatite located in interstices of the networks.
According to Kumar et al., the wiring pattern can be prevented from being subjected to the open-circuit during the sintering of the green sheet, since the sintering temperature can be lowered to less than 1,000.degree. C., for example 925.degree. C. as disclosed in an example, so as to be below the melting point of the low resistance metal which is about 1,000.degree. C. In view of manufacturing yield of the multilayer wiring substrates, however, it is desirable to further lower the sintering temperature. The green sheet is required to start its shrinkage at a temperature kept as low as possible for matching the shrinkage of the low resistance metal material which starts at 400.degree. C. But in Kumar et al. the green sheet cannot start its shrinkage at a sufficiently low temperature. Further, when the green sheets are used to make the multilayer wiring substrate, resistors are often attached to the green sheets. In this event, the green sheet is desirably selected to be of a sintering temperature matching that of the resistor for simultaneous molding of the resistor on the green sheet with the conductor. While RuO.sub.2 series resistors are considered highly reliable, it has been known that their sintering temperature is optimumly in a range of 850.degree. to 900.degree. C., so that the sintering temperature of the green sheet will be lowered below 900.degree. C., preferably to be within the range of 850.degree. to 900.degree. C. Thus, it will be appreciated that the shrink-starting temperatures matched as far as possible between the conductors, resistors and green sheets will result in a higher manufacturing freedom of the wiring pattern and an increased number of layers of the multilayer wiring substrate.
According to Kumar et al., it is an additional problem that, since the raw material may require melting in a crucible heated to about 1,500.degree. C., the crucible must be of a so-called platinum type. Thus, highly expensive manufacturing facilities will be required.
U.S. Pat. No. 4,540,671 to K. Kondo et al. discloses a sintered glass-powder product consisting of 57 to 63 wt % of SiO.sub.2, 20 to 28 wt % of Al.sub.2 O.sub.3, 10 to 18 wt % of MgO, 2 to 6 wt % of ZnO and 0.6 to 6 wt % of B.sub.2 O.sub.3 and/or P.sub.2 O.sub.5, which is sintered at a temperature of 900.degree. to 1,000.degree. C., so as to produce therein a microcrystalline cordierite quart solid solution and residual glass. This raw material is melted at a temperature of 1,400.degree. to 1,500.degree. C., allowing the use of a relatively inexpensive, so-called clay crucible.
According to Kondo et al., the melting temperature set for the raw material is below 1,450.degree. C. which makes it possible to use the inexpensive clay crucible and thus to realize inexpensive manufacturing facilities. However, Kondo et al. may still involve such a problem. The sintering temperature for the laminated ceramic substrate is still above 900.degree. C. so that simultaneous sintering of the low resistance conductor wiring pattern and resistor pattern with the green sheets of glass powder will eventually result in easy peeling-off, warp, deformation, etc., in much the same way as in Kumar et al. Thus, the rate of rejection of products will be high.